1. Field of the Invention
The present invention relates to a pneumatic wrench, and more particularly to a pneumatic wrench having a reinforced structural strength to withstand a larger torque.
2. Description of the Related Art
A conventional pneumatic wrench in accordance with the prior art shown in FIGS. 7–10 comprises a pneumatic motor (not shown), a striking mechanism 10, and a drive shaft 20. The drive shaft 20 is mounted on a socket (not shown), the striking mechanism 10 is mounted on the drive shaft 20, and the pneumatic motor is mounted on the striking mechanism 10 so that the striking mechanism 10 is mounted between the pneumatic motor and the drive shaft 20. Thus, the striking mechanism 10 is driven by the pneumatic motor to rotate in the normal direction and the reverse direction to drive the drive shaft 20 to rotate, so that the drive shaft 20 is driven to rotate the socket mounted on the drive shaft 20 so as to drive and rotate a screw member, such as a bolt, nut or the like.
The striking mechanism 10 includes a cylindrical support seat 11 having a closed first end face and an open second end face, a cam 15 rotatably mounted on the first end face of the support seat 11 and engaged with and rotated by the pneumatic motor, a cover 18 mounted on the second end face of the support seat 11, and a substantially arc-shaped hammer 16 rotatably mounted in the support seat 11 and engaged with the cam 15 so that the hammer 16 is driven by the cam 15 to rotate in the support seat 11. The hammer 16 has a side face having a mediate portion formed with an axially extended protruding pivot shaft 17 pivotally mounted in the support seat 11. The pivot shaft 17 of the hammer 16 has a first end formed with a first pivot shaft 170 pivotally mounted in the first end face of the support seat 11 and a second end formed with a second pivot shaft 172 pivotally mounted in the cover 18. The first end face of the support seat 11 has a central portion formed with a shaft hole 12 for mounting the cam 15. The support seat 11 has an inner wall formed with an axially extended pivot slot 13 for mounting the pivot shaft 17 of the hammer 16. The first end face of the support seat 11 has a periphery formed with a pivot hole 14 communicating with the pivot slot 13 for mounting the first pivot shaft 170. The cover 18 has an end face having a periphery formed with a pivot hole 19 for mounting the second pivot shaft 172. The drive shaft 20 has a first end formed with an engaging portion 25 engaged with the hammer 16 and a second end formed with a mounting section 22 for mounting the socket. The engaging portion 25 of the drive shaft 20 is formed with a driven groove 26 engaged with and driven by the hammer 16 so as to produce a striking effect on the drive shaft 20 by rotation of the hammer 16.
In operation, after the compressed air enters the pneumatic motor, the pneumatic motor is operated to rotate the cam 15 which engages the hammer 16 so that the hammer 16 is driven by the cam 15 to pivot in the support seat 11. Thus, the hammer 16 is pivoted to strike the drive shaft 20, and the hammer 16 strikes the drive shaft 20 once when the hammer 16 is rotated through a circle, so that the drive shaft 20 is driven to rotate the socket mounted on the mounting portion 22 of the drive shaft 20 so as to drive and rotate a screw member, such as a bolt, nut or the like.
However, the hammer 16 is substantially arc-shaped so that most of the stress of the hammer 16 is concentrated on the two opposite sides 160 of the hammer 16 during operation of the hammer 16, so that the hammer 16 is easily distorted or broken during a long-term utilization, thereby decreasing the lifetime of the hammer 16. In addition, the first pivot shaft 170 is pivotally mounted in the pivot hole 14 of the support seat 11, and the second pivot shaft 172 is pivotally mounted in the pivot hole 19 of the cover 18 so that the first pivot shaft 170 and the second pivot shaft 172 are subjected to a shear stress to produce concentration of a stress, thereby deforming or breaking the hammer 16 during the striking process.